In the past two years, I have purified human methylmalonyl-CoA mutase to homogeneity and iodinated the protein. Utilizing antibodies raised in chickens, I have developed a sensitive radioimmunoassay for the enzyme protein. Utilizing this radioimmunoassay I have determined the level of methylmalonyl-CoA mutase enzyme protein in normal fibroblasts and a variety of fibroblasts from patients with congenital methylmalonicaciduria. These studies revealed considerably more genetic heterogeneity than was previously suspected. Further studies will be performed utilizing the radioimmunoassay to determine the regulation of enzyme protein synthesis in normal cells and in cells from these patients with a variety of genetic defects in methylmalonyl-CoA mutase. These results could have important therapeutic implications for this genetic disorder. We have recently performed studies which indicate that exposure of animals to nitrous oxide anesthesia results in the production of cobalamin analogues as well as marked inhibition of both methionine synthetase and methylmalonyl-CoA mutase. In addition, have developed cobalamin analogues which are capable of inhibiting methionine synthetase activity upon injection into rats. We plan to utilize exposure to nitrous oxide anesthesia, injection of inhibitory cobalamin analogues and diets deficient in methionine, cobalamin, and folate to determine if tumor growth in rats is decreased compared to control animals.